System for injecting composite substance inside a forming mould

ABSTRACT

A system for injecting a composite substance inside a forming mould comprising a supplying device and at least one measuring device and which includes at least one line formed of articulated tube sections which are double-sheathed so as to enable a heat exchanging fluid to circulate therein. The system enables limitation of head loss and control of temperature of the composite substance. A device injecting the substance inside the mould can be mounted on a movable part of the mould.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system for injecting composite substancesinside a forming mould.

2. Description of the Related Art

A composite moulding substance generally comprises a resin andappropriate reinforcing fibers or fillers. Patent Application FR-A-2 629388 discloses an apparatus for injecting composite substance inside aforming mould, comprising one or more measuring devices, of the typeincorporating a mobile piston, connected to a common supply device,likewise of the piston type, each measuring device being associated withan injection device mounted on the mould. This device is efficient formoulding composite substances comprising a thermosettable resin.

However, thermosettable resins have a relatively high density, of theorder of 1.4 to 1.9, and generally do not make it possible to assemblethe pieces made by a simple cooperation of shape, i.e. by clipping. Now,such a clipping may be desirable for bodywork or structural elements ofan automobile vehicle, such as a radiator grill, a wing or an interioror exterior fitting. It has therefore been envisaged to usethermoplastics resins whose density is lower and which allow fixation ofthe pieces by elastic deformation.

One constraint of thermoplastics resins resides in the fact that theymust be injected in the forming mould at a temperature of the order of220 to 290° C., the pressure of moulding being of the order of 300 to350 bars. These values are substantially higher than the correspondingvalues for thermosettable resins, which are about 170° C. and from 100to 250 bars, respectively.

On the other hand, as a function of the geometry of the piece to bemoulded, it is sometimes necessary that the injection device beinstalled on a mobile part of the mould in order that the mark possiblyleft on the finished piece at the point of injection be located in aconcealed part of the piece once the latter is mounted. It is thennecessary to provide a system of supply moulding substance to theinjector which allows for movements of the latter due to the movementsof the mould. It has been envisaged to install in the known device ofFR-2 629 388 a flexible pipe between the measuring device and theinjection device.

However, such a flexible pipe should be made with a reinforced pipewhich is particularly expensive. Moreover, the geometry of the pipewould vary as a function of the position of the mobile part of themould, with the result that the head losses induced by this pipe wouldbe considerable and variable. Moreover, the known technology does notmake it possible to use flexible pipes of large diameter at thepressures envisaged, with the result that the head losses induced in aflexible line are considerable. It is then necessary that the commonsupply device operate at very high pressure in order to attain, at thelevel of the impression of the mould, the necessary 300 to 350 bars whenmoulding a thermoplastics resin.

In addition, a flexible line necessarily comprises two connectionsallowing it to be connected at its two ends to a fluid circuit. Suchconnections necessarily present a reduction in the internal diameterwith respect to that of the flexible pipe, this inducing additional,likewise inadmissible head losses.

Furthermore, one of the principal advantages of composite substancesbased on thermoplastics resins is that they may contain relatively longfibers, i.e. whose length may exceed 20 mm. Now, in a system providedwith a flexible pipe, the long fibers risk being broken when passing theconnections. Finally, whatever precautions are taken at the level of thesupply or measuring devices, the temperature of the substance to beinjected cannot be controlled when it transits in the flexible pipe, thelatter being able to be several meters long, with the result that heatexchanges lead to the reduction in the temperature of the compositesubstance, which is detrimental to its fluidity and moulding properties.

U.S. Pat. No. 5,540,580 describes a system for injection ofnon-reinforced plastics material, provided with a supply line formed byarticulated sections. The temperature control of the material in thisline is provided by means of systems involving a small internal diameterof the line, hence considerable head losses.

SUMMARY OF THE INVENTION

The invention aims at solving these problems and at proposing a systemof injection of composite substance capable of functioning withthermoplastics resins or thermosettable resins, including in the case ofthe injector being placed on a mobile part of the mould.

In this spirit, the invention relates to a system of injection ofcomposite substance inside a forming mould, said system comprising asupply device equipped with a piston, at least one measuring device alsoequipped with a piston, and at least one line for supplying the mouldwith composite substance, characterized in that said line presents asubstantially constant internal cross-section and is formed byarticulated tube sections, said tubes being double-sheathed so as toallow the circulation of a heat-exchange fluid.

Thanks to the invention, the head losses induced in the line formed byarticulated tube sections may be determined with great precision,particularly by calculation, and remain substantially constant whateverthe position of this articulated line. In effect, the tubes conserve asubstantially rectilinear constant geometry whatever their relativepositions. Moreover, the circulation of a heat-exchange fluid makes itpossible to maintain the composite substance injected at a temperaturesuitable for the moulding process, including when the articulated linehas a length of several meters. Finally, the line formed by articulatedtube sections does not comprise any connection with internalcross-section reduced with respect to the rest of the line, with theresult that the fibers included in the substance to be injected do notrisk being broken when passing such connections. The substantiallyconstant internal cross-section of the line guarantees that no shear ofthe fibers takes place during the movements of the articulated line.

According to a first advantageous aspect of the invention, the lineformed by articulated tube sections includes at least one rotatingconnection adapted to resist fluid pressures of the order of 350 bars.The use of a rotating connection makes it possible to obtain a degree offreedom necessary for the function of articulation of the line withouthaving a negative influence on the head losses induced by the latter. Inthat case and according to another advantageous aspect of the invention,the rotating connection comprises a male sleeve penetrating in a femalesleeve, these sleeves together defining an interstice provided withballs and each being associated with a bend. This constructionguarantees that the rotating connection withstands the desired pressuresand allows the articulation of the line of the system of the invention.

According to another advantageous aspect of the invention, the internalcross-section of the line formed by sections of tubes, is substantiallyconstant. This makes it possible to maintain the head losses induced, ata minimum level.

According to a first embodiment of the invention, the line formed bytube sections is interposed between the measuring device and the mould.According to a second embodiment of the invention, the line formed bytube sections is interposed between the supply device and the measuringdevice. In that case, it may be provided that the measuring device befixed on a mobile part of the mould. It thus forms with the injectiondevice a compact assembly inside which the head losses and thevariations in temperature may be optimized at their minimum values.

According to another advantageous aspect of the invention, the systemcomprises at least one injector mounted in the mould, this injectorcomprising a space for circulation of heat-exchange fluid up to theimmediate proximity of the opening of the injector. This aspect of theinvention makes it possible to control the temperature of the compositesubstance injected, up to its introduction in the mould.

According to another advantageous aspect of the invention, a thermalconnection is placed around the injector in the mould. This aspect ofthe invention makes it possible to maintain the substance to be injectedat a temperature different from that of the mould, up to its point ofinjection in the mould.

According to another advantageous aspect of the invention, the supplydevice and/or the measuring device and/or the injection device aredouble-sheathed so as to allow circulation of a heat-exchange fluid.This aspect of the invention thus makes it possible, in cooperation withthe line formed by double-sheathed tubes, to control the temperature ofthe substance to be injected all along the injection line.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood and other advantagesthereof will appear more clearly in the light of the followingdescription of two embodiments of a system for injection of compositesubstance in accordance with its principle, given solely by way ofexample and made with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a system for injection of composite substanceaccording to a first embodiment of the invention;

FIG. 2 is a transverse cross-section of a rotating connection and of theend of two tubes belonging to the device of FIG. 1;

FIG. 3 is a view in section of the terminal part of an injection deviceused with the system of FIG. 1; and

FIG. 4 is a view similar to FIG. 1 for a system according to a secondembodiment of the invention.

The system for injection of composite substance shown in FIG. 1comprises a reservoir 1 in which is temporarily stored a compositesurface which may be made from thermosettable resin, such as polyester,vinylester or a phenolic resin, or from thermoplastics resin, such as aresin belonging to the polyolefin family. This resin may be reinforcedwith reinforcing fibers based on glass, carbon or any other suitablematerial. An Archimedean screw 2 is disposed at the foot of thereservoir 1 and controlled by a motor 2 a in order to convey thesubstance to be injected up to a supply device 3 provided with a packingpiston 4. At the outlet of the supply device 3 there is connected ameasuring device 5 likewise equipped with a piston 6, pistons 4 and 6are displaced by means of electrical or pneumatic devices known to theperson skilled in the art, their position being able to be detected bymeans of encoders or any other equivalent means.

The substance is injected in a mould 10 formed essentially by a mobiledie 11 and a fixed punch 12. The die 11 is periodically moved apart fromthe punch 12 in order to allow the moulded pieces to be removed. Aninjection device 13 is connected with the interior volume 10 a of themould thanks to a bore 14 made in the die 11. The injection device maybe of any known type and, in particular, be in accordance with thetechnical teaching of EP-A-0 606 037.

According to the invention, between the measuring device 5 and theinjection device 13 there is inserted a line 20 formed by tube sections21 connected together by rotating connections 22. The tubes 21 aredouble-sheathed including a composite carrying tube 21 and a generallyconcentric surrounding heat exchange tube 21′, with the result that aheat-exchange liquid, such as an oil based on a mixture of syntheticalkylbenzenes can circulate in tube 21′, as represented by arrows F. Theoil based on synthetic alkylbenzenes has the noteworthy property ofwithstanding high temperatures, or the order of 290° C., withoutnoteworthy degradation. In the same way, it may be provided that theArchimedean screw 2, the supply device 3, the measuring device 5 and/orthe injection device 13 be double-sheathed so as to allow thecirculation of a heat-exchange fluid, this likewise being represented byarrows F in FIG. 1. The heat-exchange fluid may be the same as thatdescribed hereinabove, in which case a common heat-exchange fluid supplycircuit may be provided; it may also be question of anotherheat-exchange fluid, which makes it possible to maintain these differentenclosures at temperatures different from one another.

The rotating connections 22 serving for articulation are adapted towithstand fluid pressures of the order of 350 bars. to that end, and asis more clearly apparent in FIG. 2, they comprise a female sleeve 30 anda male sleeve 31 on which are respectively fixed two bends 32 and 33,these bends themselves being connected to two tubes 21. The bends 32 and33 are welded on the sleeves 30 and 31, the welding beads beingreferenced 34. A joint by welding allows this assembly to withstand highpressures. An interstice 35 is formed between the sleeves 30 and 31, itdefines circular grooves in which may be inserted balls 36 by means ofopening closed by stoppers 37. O-rings 38 are disposed in grooves 39 ofthe male sleeve 31, near the ends of the interstice 35. This rotatingconnection therefore allows a relative movement of two tubes 21 in theplane of FIG. 1. It will be noted that the internal cross-section of thetubes 21, the bends 32 and 33 and the sleeves 30 and 31 is substantiallyconstant, with the result that the presence of the rotating connections22 in the line formed between the measuring device 6 and the injectiondevice 13 does not induce any specific head losses, which is essentialat the pressures of use in question. Moreover, the fibers contained inthe composite substance do not risk being broken when passing theserotating connections.

The injection device or injector, partially shown on a larger scale inFIG. 3, is mounted on the mobile die 11. In its terminal part, itcomprises a space 15 for circulation of a heat-exchange fluid such asthe oil mentioned above. This space 15 may be provided with internalfins or ribs 15 a intended to promote guiding of the heat-exchangerliquid up to the immediate proximity of the opening 13 a of the injector13, as well as the heat exchanges. These ribs 15 a may in particularhave a helicoidal form. In this way, the temperature of the compositesubstance to be injected may be controlled up to its point of injectionin the internal volume 10 a of the mould 10. This is particularlyadvantageous in the case of a composite substance based onthermoplastics resin being used, insofar as the mould 10 is maintainedat a temperature of the order of 70° while the thermoplastics materialis injected at a temperature of the order of 250° C. The heat-exchangefluid present in the space 15 therefore enables the thermoplastics resinto be heated.

In the case of use of the device of the invention with a thermosettableresin, the mould is heated to a temperature of the order of 170° C,while the resin is injected at a temperature of the order of 70° C. Inthat case, the circulation of heat-exchange liquid in space 15 makes itpossible to cool the substance before it is injected in the volume 10 a.

In order to facilitate maintenance of the substance to be injected at atemperature different from that of the mould, it may also be providedthat a heat-insulation connection 16 be placed around the injector 13 inthe die 11, with the result that it limits the heat-exchanges betweenthe injector 13 and the mould 10.

In the second embodiment of the invention shown in FIG. 4, elementssimilar to those of the embodiment of FIGS. 1 to 3 bear identicalreferences. This embodiment differs from the preceding one essentiallyin that the measuring device 5 is installed on the mobile die 11 of themould 10, with the result that circulation of composite substance to beinjected between the measuring device 5 and the injector 13 takes placeover a minimum distance. This contributes to a better precision ofmeasurement. In that case, the line 10 formed by sections of tubes 21 isinterposed between the supply device 3 and the measuring device 5. Itperforms the same function as before, allowing the relative movements ofthe die 11 with respect to the punch 10 without inducing inadmissiblehead losses or variations in temperature not compatible with the processcarried out.

Whatever the embodiment of the invention, a plurality of measuringdevices 5 may be associated with a single common supply device 3. Aplurality of lines 20 are in that case used in parallel.

What is claimed is:
 1. System for injection of thermoplastic andthermosettable composite resin substances which include reinforcingfibers, the system including a forming mold, a supply device equippedwith a piston, at least one measuring device equipped with a piston, atleast one line for supplying said forming mold with a composite resinsubstance connected between said supply device and said forming mold,said at least one line including a plurality of articulated tubesections connected to one another by pairs of spaced bends and anintermediate rotable connection sleeve, each of said plurality ofarticulated tube sections being double sheathed having an innercomposite conducting tube and an outer sheath spaced from andsurrounding said inner composite conducting tube to thereby define acirculation heat exchange passageway therebetween, each of said innercomposite conducting tubes of said plurality of articulated tubesections, bends and rotable connection sleeves having equal and constantinternal cross-sections so as to not induce head losses and to reducerisk of fiber damage, and means to allow circulation of a heat-exchangefluid within each said circulation heat exchange passageway.
 2. Systemfor injection according to claim 1 wherein each said rotable connectionsleeve includes a male sleeve penetrating in a female sleeve, said maleand female sleeves defining therebetween an interstice provided withballs and each of said male and female sleeves being connected to one ofsaid bends.
 3. System for injection according to claim 1, wherein saidsupply device, said at least one measuring device and said mold aredouble sheathed to create areas for circulation of a heat exchangefluid.
 4. System for injection according to claim 1 wherein said atleast one line is interposed between said at least one measuring deviceand said mold.
 5. System for injection according to claim 1, whereinsaid at least one line is interposed between said supply device and saidat least one measuring device.
 6. System for injection according toclaim 1, wherein at least one of said at least one measuring device,said mold, and said supply device is double sheathed to create an areafor circulation of a heat exchange fluid.
 7. System for injection ofthermoplastic and thermosettable composite substances which includereinforcing fibers, the system including a forming mold, a supply deviceequipped with a piston, at least one measuring device equipped with apiston, at least one line for supplying said forming mold with acomposite resin substance connected between said supply device and saidforming mold, said at least one line including a plurality of tubesections which are connected to one another by a pair of spaced bendsand an intermediate rotable connection between each pair of bends, eachof said articulated tube sections being double sheathed having an innercomposite conducting tube and an outer sheath spaced from andsurrounding said inner composite conducting tube to thereby define acirculation heat exchange passageway therebetween, each of said innercomposite conducting tubes, said pairs of spaced bends and saidintermediate rotable connection sleeves having internal cross sectionswhich are equal and constant therethrough, at least one injector mountedin said mold, a sheath provide about said at least one injector defininga space surrounding said injector for circulation of heat-exchange fluidwhich space extends into proximity of an opening of said at least oneinjector into said mold.
 8. System for injection according to claim 7,wherein a heat-insulation connection is placed around said at least oneinjector.
 9. System for injection according to claim 7 wherein saidsupply device and said at least one measuring device are double-sheathedso as to allow circulation of a heat-exchange fluid about inner chambersof said supply device and said at least one measuring device.